Start with a rectangle 20 cm by 25 cm. Its area is A = LW = 20 cm * 25 cm = 500 cm^2
Now look at the two circular parts. Each circular cutout is a half circle, so both combined have the area of a circle. You must subtract the area of the circle from the rectangle whose area we found above. To find the area of a circle, we need its radius. Look at the right side of the rectangle. Its length is 25 cm. The 4 small vertical segments next to the semicircles have a single mark through them. That means they are all congruent. The lower left segment has length 4.5 cm, so all short vertical segments have length 4.5 cm. Look again at the right side. The vertical side has length 25 cm. Subtract the two 4.5-cm segment lengths, and the diameter of the semicircle is 25 cm - 4.5 cm - 4.5 cm = 16 cm. The radius is half the diameter, so the radius is 8 cm.
The shaded area is the area of the rectangle minus the area of the circle. Area of circle = pi * r^2
Shaded area = 500 cm^2 - (8 cm)^2 * pi
The exact area is: [tex] Shaded ~area = (500 - 64\pi)~cm^2 [/tex]
An approximation of the area is: [tex] Shaded ~area = 298.9~cm^2 [/tex]